Summary
MLA contracted CSIRO, from 2010 to 2013, to assess biological control agents of parkinsonia (Parkinsonia aculeata) to determine if they were likely to be environmentally safe and effective as control agents. Parkinsonia has been identified as one of the most serious weeds of the northern beef industry and also as a high priority candidate for biocontrol. This project was based on a previous MLA funded phase I project which identified the ten most likely candidates following preliminary assessment in the native range. The purpose of this phase II project was to determine if the top three agents were sufficiently specific and safe to release in Australia and to apply for the relase of those that were. Previous evidence suggested that at least one of these agents would be suitable. Hence this project was expected to result in release of at least one agent to assist in the management of this weed. Biocontrol agents can control weeds by damaging their structures and reducing growth rates, survival rates, reproductive output, rates of spread and competitiveness.
We exceeded these objectives by determining the suitability of all ten highest priority agents, and an eleventh species that was discovered during the course of this study. Over the three years of this project, six were excluded from further consideration following work in the native range and five species were imported into Australian quarantine for more intensive assessment. All five species studied only in the native range were eliminated on the grounds of being too rare to work with, not adequately damaging, not being sufficiently specific or being too difficult to breed or test. Two of the five quarantine-tested insects could not be satisfactorily tested as they could not be reared even on the target weed, and a third one failed testing as it was not adequately specific.
The remaining two species tested in Australian quarantine were deemed acceptable for release on the basis that they were both damaging and specific to the target plant. In laboratory tests, full development of egg to adult occurred consistently on parkinsonia with a high rate of success (average of 50%). But no development occurred on any of the 60-plus test plant species. All larvae died in the first stage of their development. No feeding occurred on any test plant species and hence no damage was observed on non-target species. We concluded that the level of risk associated with releasing both agents into the Australian environment was acceptable and that they will potentially be effective biological control agents for parkinsonia. Following this we sought permission for their release in Australia.
Both of these agents are looper caterpillars of the family Geometridae. The first of these loopers, Eueupithecia cisplatensis, nicknamed UU, has been approved for release and preliminary test releases have been made in Northern Australia. It is too early to know the results of the releases. The second agent, the related Eueupithecia sp.2, nicknamed U2, is the subject of a pending application for release. Given that U2 is as specific as UU, it is expected to be approved. The larvae of both agents feed on leaves of their host plant. Leaf feeding by larvae reduces the total photosynthetic area of the plant causing a reduction in vigour, growth rate and seed production. In the laboratory the larvae are voracious feeders and completely strip all foliage from plants. As the leaves of parkinsonia are undamaged in Australia, the potential for impact on the plant is great.
No further biocontrol agents of parkinsonia are known, so it is imperative to maximise the establishment and impact of these two with a thorough release project. An application for funding to the WA Cattle Industry Funding Scheme for the release and evaluation of the parkinsonia loopers in Western Australia was successful and that project has commenced with releases being made in the Kimberley and Pilbara regions in May 2013. An initial release has also been made in Queensland in April 2013. A colony has been provided to Queensland and Northern Territory colleagues so that these agencies are ready to contribute to the future national release project for which funding has been sought from MLA. The state and territory collaborators will collaborate in future rearing and release efforts. As field populations of parkinsonia in Australia are patchy and disjunct, a large effort will need to be made to achieve extensive establishment. The proposed national-scale field trial will help ensure that this is achieved efficiently and effectively by optimising release-sizes, stages (adults, larvae or eggs), timing and locations. Once establishment is achieved, populations are expected to be self-sustaining, but ongoing evaluation will be required to quantify the success of biocontrol and to identify any ways that impacts can be further improved.
In addition to achieving all its milestones, this project and its predecessor generated a long list of publications of both an applied and basic nature that contribute to the practise of biological control and will make it more efficient and effective in the future.
